Multiple-Input Multiple-Output (MIMO) transmission systems can provide multiplexing gain, diversity gain, and antenna gain. Therefore, the technology of MIMO has been applied in many recent communication standards, such as IEEE 402.11n, IEEE 402.16, and 3GPP Long-Term Evolution (LTE). However, there exist bottlenecks in the technology of MIMO in terms of higher complexity and increased hardware cost.
In order to alleviate these drawbacks of MIMO systems while preserving its advantages such as high spectral efficiency, a new modulation method for the MIMO systems, called Spatial Modulation (SM), has recently been proposed. Spatial modulation can reduce system complexity and hardware cost while maintaining data transmission rate. Spatial modulation can be a new modulation technique in the physical layer mainly because of the following features. First, low complexity and low cost. For point-to-point transmission, only one antenna is activated for data transmission at any time. This enables spatial modulation while avoiding inter-channel interference. It does not require a synchronization process for multiple antennas, but requires just one RF link, and a receiving end only needs to receive one information flow, so that a simple detection algorithm can be applied directly. Second, additional modulation orders. For example, Nt antennas can bring an additional modulation order of log2(Nt). Therefore, although just one antenna is activated at each time slice, spatial modulation can still provide a very high data transmission rate.
Spatial modulation can be used for point-to-multipoint multi-user transmission, and corresponding typical application scenarios include, for example, downlink multi-user transmission in a cellular communication system, where the base station is often equipped with a larger number of antennas to facilitate spatial modulation. Therefore, how to realize spatial modulation for point-to-multipoint multi-user transmission has become one of the research hotspots in this field.